For manufacture of polyolefin having high strength and modulus, Japanese Patent Laying-Open No. Hei. 1-280013 discloses a method wherein ultra-high molecular weight polyethylene and a flow modifier such as paraffin wax are melt kneaded at a temperature above a melting point of the ultra-high molecular weight polyethylene and extruded from a die into a shaped article which is subsequently subjected to multi-stage stretching. The publication states that such a method permits the highly productive and simple manufacture of ultra-high molecular weight polyethylene having high strength and modulus on an industrial scale.
However, the method described in the above-identified publication requires the use of a solvent to remove the flow modifier either during or subsequent to the stretching process. This not only adds to operating time but also poses a problem of increased manufacturing cost resulting from the need to use the solvent for removal of the flow modifier.